Put BTDSys RingMod.dll in your Gear\Effects folder.
RingMod is a ring modulator effect, ie it multiplies together its input signals. Unlike other Buzz ring modulators, which either use auxbus or internal oscillators for one of the signals, RingMod multiplies any number of inputs connected directly to it.
This machine is really simple, and I'm tired, so that's all the docs you're getting :)
Docs and code ŠEd Powley (BTDSys)